The invention relates to fluid flow machines in general, and more particularly to improvements in fluid flow machines of the type wherein a pump (such as a reciprocating piston type liquid pump) is operated by a pneumatic motor. Still more particularly, the invention relates to improvements in fluid flow machines of the type wherein the motor (normally a double-acting motor) is spaced apart from the pump and its operation is controlled by a regulating unit serving to effect the admission of pressurized fluid into and the evacuation of fluid from the chambers at opposite sides of the reciprocable piston of the motor.
Fluid flow machines of the above outlined character are often employed to bring about pronounced pressurization of liquid by resorting to a pneumatic motor wherein the admitted gaseous fluid is maintained at a relatively low pressure. Such machines are used in grease guns, hydraulic clamping devices and the like. Another very important field of application of such fluid flow machines is in conjunction with hydrostatic spray guns for liquid paints and many other types of flowable materials. The purpose of a fluid flow machine which cooperates with a spray gun is to deliver to the latter a stream of highly pressurized flowable material which is to be sprayed subsequent to electrostatic charging of its droplets or particles. For example, a so-called airless hydrostatic spray gun must receive a stream of the material to be sprayed at a pressure of 30-300 bar, depending on the nature of the material to be sprayed and on the presence or absence of means for supplying additional air (the technique relying on the utilization of additional air is known as the "airless plus" method).
A presently known fluid flow machine which is used to deliver pressurized flowable material to a spray gun is shown and described on page 12 of a brochure entitled KOPPERSCHMIDT-MUELLER Geratetechnik (published Oct. 1983 and distributed by the assignee of the present application). The fluid flow machine which is described and shown in this brochure has a liquid-containing chamber which is disposed above the pump and beneath the motor and contains a supply of multiple-purpose liquid which is to prevent penetration of conveyed flowable material from the pump into the motor as well as to lubricate the parts which transmit motion from the piston of the pneumatic motor to the pump piston. The piston rod of the pump extends from the pump housing whenever it performs a working stroke, and the purpose of the liquid in the aforementioned chamber is to clean the piston rod of the pump as well as to lubricate the piston rod to thereby prolong the useful life of the pump and of the entire fluid flow machine. The liquid in the chamber contributes significantly to longer useful life of the sealing means in the region where the piston rod of the pump extends from the pump housing as well as of the sealing means which serves to prevent penetration of particles of paint or other material to be sprayed all the way into the interior of the pneumatic motor. If the material to be sprayed is a paint or any other hardenable substance, fragments of hardened material are especially likely to affect the fluid confining action and useful life of seals for movable parts of the pump and/or for movable parts of the motor.
The pump of the aforementioned fluid flow machine is spaced apart from the motor because the device which connects the piston rod of the pump piston with the piston rod of the piston in the housing of the motor should not contact the motor seal and/or the pump seal when the machine is in use, i.e., when the piston of the motor is reciprocated by a pressurized gaseous fluid to thereby reciprocate the pump piston so that the latter can draw and pressurize the material to be sprayed. As a rule, the chamber for the rinsing and lubricating medium is disposed above the pump housing, and the level of its top wall is determined by the upper level of the supply of liquid medium therein. The top wall of the chamber is spaced apart from the bottom end wall of the motor housing by a distance which suffices to provide between such walls a space (called lantern space) wherein the aforementioned connecting device can reciprocate and into which the piston rod of the motor can extend when the machine is in use so that the piston rod of the pump does not come in contact with the material which is conveyed and pressurized by the pump.
The means for regulating the flow of pressurized gaseous fluid to, and the flow of spent gaseous fluid from, the motor chambers of the machine which is described in the aforementioned brochure is outwardly adjacent and is disposed at one side of the motor housing. Such regulating means employs several valves which are actuated by the reciprocating piston of the pneumatic motor. A drawback of such design is that the regulating means contributes to the bulk of the fluid flow machine, particularly to the floor space requirements of the machine. Moreover, the machine is rather noisy and the motor housing must be formed with two additional openings for the valve actuating means.
A modified fluid flow machine is disclosed in German Offenlegungsschrift No. 33 42 388 of Willig. The means for regulating the flow of gaseous fluid to and from the chambers of the pneumatic motor is installed at a level above the motor. A mechanical connection is provided to transmit motion from the piston rod of the motor to the moving parts of the regulating means. To this end, it is necessary to provide an opening in one end wall of the motor housing and to adequately seal such opening around the motion transmitting part. Willig further proposes to employ the space around the regulating means as an expansion chamber for air which flows from the chambers in the motor housing to thus achieve a certain reduction of noise. An additional drawback of the proposal of Willig is that the overall length of the machine is increased by the height of the regulating means above the motor and that the height of the regulating means itself is excessive.